Are worm lizards closely related to snakes?

“Worm lizards” – lizards without legs or with small legs – look very much like snakes. But are they closely related to each other? A fossil lizard uncovered in Germany says “no.” Professor Johannes Müller of Humboldt-Universität, Berlin, who led the team that studied the fossil, said in a press release dated May 18, 2011,

This fossil refutes the theory that snakes and other burrowing reptiles share a common ancestry and reveals that their body shapes evolved independently.

Their findings were reported in the May 19, 2011 issue of Nature.

The fossil, Cryptolacerta hassiaca, was a small lizard with legs that lived 47 million years ago in modern-day Germany. It showed anatomical similarities to worm lizards called Amphisbaenia. In particular, it had a thick reinforced skull needed for burrowing head-first into the ground. Its thick skull also indicated that for worm lizards, head-first burrowing evolved before the development of a long snake-like body.

Because of their physical similarities, some scientists have thought that worm lizards and snakes are closely related to each other. DNA studies, however, indicate that worm lizards are closely related to lacertids, a type of lizard with limbs found in Europe, Africa, and Asia. Meanwhile, genetic studies of snakes show they’re closely related to monitor lizards and iguanas.

Cryptolacerta hassiaca was a small lizard with legs that lived 47 million years ago. Comparisons of its features to living lizards suggest that it lived among leaf litter and was an opportunistic burrower. X-ray computed tomography (CT) imaging and an inspection of its skeleton revealed that Cryptolacerta had many features in common with both worm lizards and lacertid lizards – it could well have been an early evolutionary stage of worm lizards. The paper in Nature also included a study of anatomical features of Cryptolacerta and other lizards, as well as DNA studies of living lizards and snakes, to better understand how these reptiles are related to each other.

The controversial evolutionary relationship between worm lizards and snakes has been given some clarity by a fossil lizard with legs named Cryptolacerta hassiaca that lived 47 million years ago. Features in worm lizards and its close genetic relative, old world lacertid lizards, were found in the fossil, supporting DNA evidence that snakes and worm lizards evolved separately. Cryptolacerta‘s thick skull, made for burrowing head-first into the ground, suggests that the adaptation for burrowing evolved before its elongated snake-like body.

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